The present invention relates to an inkjet recording apparatus, and more particularly to an inkjet recording apparatus having a so-called linear inkjet head.
Recently, inkjet printers have been widespread since they generate less noise, and use standard paper as recording medium. A conventional inkjet printer typically employs a movable inkjet head which sweeps in a width direction (main sweeping direction) of the recording medium, which moves relative to the inkjet head in a direction (auxiliary sweeping direction) perpendicular to the main sweeping direction to form a two-dimensional image on the recording medium. Such an inkjet head is referred to as a serial type inkjet head.
In such an inkjet printer, since the inkjet head moves, an image forming speed is limited to a certain level, and is difficult to meet a recent demand of high-speed imaging. To meet such a demand, usage of a linear inkjet head attracts attention. The linear inkjet head is provided with a plurality of ink ejecting nozzles arranged in a width direction (i.e., the main sweeping direction) of the recording medium. Typically, the linear inkjet head is fixed at a predetermined position of the printer, while the recording medium is driven to move at a high speed in the auxiliary sweeping direction, thereby the imaging speed being greatly accelerated.
Incidentally, ink residing at the ink ejecting nozzles of the inkjet head tends to dry easily since it is exposed to the air. Therefore, before a printing job, and may also be during the printing job, a flushing operation for forcibly removing the residual ink at the ink ejecting nozzles may be performed.
If the inkjet head is a serial type (i.e., the movable type), a flushing position is defined, which is a position outside an imaging area for the recording medium, and the flushing operation is performed with the inkjet head located at the flushing position.
However, if the inkjet head is a linear head, it is difficult to perform the flushing operation by moving the inkjet head to a position outside the imaging area of the recording medium since a wide space for allowing the inkjet head to move and a highly accurate driving mechanism to move the inkjet head between the imaging position and a flushing position should be provided. A method in which a member that collects the forcibly discharged ink is moved to the inkjet head at every flushing operation has once been suggested. However, such a method also requires a space and a mechanism for moving the ink collecting member. Further, it takes time to execute such a flushing operation, and is not suitable for the purpose of improving the imaging speed.
Japanese Patent Provisional Application No. 2001-71521 shows an exemplary configuration to cope with such a problem. In this publication, a rotatable cylindrical member having a slot, which is through-bored along the diameter and is elongated in the axial direction of the cylindrical member, is provided immediately below an inkjet head. Further, an ink absorbing member is provided so as to face the inkjet head with the rotatable cylindrical member therebetween. When the flushing operation is performed, the rotatable cylindrical member is rotated so that the inkjet head and the ink absorbing member face each other through the slot, and the ink discharged by the inkjet head is absorbed by the ink absorbing member.
Another configuration disclosed in Japanese Patent Provisional Publication No. HEI 63-160850 includes an ink absorbing member which faces the ink ejecting orifices, and a retractable platen is provided between the inkjet head and the ink absorbing member. In this configuration, when the flushing is performed, the platen is retracted from the position between ink ejecting orifices and the ink absorbing member so that the ejected ink is absorbed by the ink absorbing member.
Even in the configurations disclosed in the above publications, operations dedicated only to the flushing operation are required, and it may take several seconds to perform the flushing operation. If, for example, an imaging speed of an inkjet printer is 120 sheets/minute, and a flushing operation is performed at every completion of imaging on a sheet, the imaging speed is decelerated to approximately 20 sheets/minute due to the flushing operations. Thus, image formation speed is fast but the effective imaging speed including the flushing operation cannot be sufficiently accelerated.
As such, an improved inkjet recording apparatus which can execute the flushing operation without decelerating the recording speed has been desired.
The present invention is advantageous in that an inkjet recording apparatus employing a linear inkjet head and is capable of performing a flushing operation without decelerating an imaging operation can be provided.
According to an aspect of the invention, there is provided an inkjet recording apparatus that records an image on recording medium, the recording medium being fed in a predetermined direction which is perpendicular to a width direction of the recording medium, which is provided with at least one inkjet head having a plurality of groups of nozzles that eject the ink, and a platen closely arranged to face the at least one inkjet head, the platen having a main body. The plurality of groups of the nozzles are arranged in a width direction of the recording medium with predetermined clearances therebetween, and parts of the plurality of groups overlap when viewed from a direction in which the recording medium is fed so that the plurality of groups are continuously provided as a whole. Further, a plurality of protrusions are formed on the main body of the platen at locations facing the clearances between the plurality of groups of the inkjet head.
When the flushing operation is performed, the ink is ejected from the nozzle groups toward platen at portions other than the protrusions, while when the imaging operation is performed, the recording medium is supported by the protrusions. Thus, the flushing operation can be performed without requiring a dedicated moving mechanism such as the ink collecting device or moving the inkjet head to a particular position for the flushing. Accordingly, the flushing operation can be performed within a relatively short period of time, and the effective imaging speed of the inkjet recording apparatus will not be significantly decreased.
Optionally, ink absorbing members may be arranged on the main body at locations facing the groups of inkjet nozzles, ink ejected from the plurality of groups being absorbed by the ink absorbing members.
Alternatively, the main body may be formed with through-openings at locations corresponding to the plurality of nozzles of the inkjet head, and the ink ejected from the plurality of nozzles is removed through the through-openings.
Optionally, a plurality of ink absorbing members may be provided at the plurality of through-openings, respectively.
Further optionally, a suction device may be connected to the main body, the ink ejected by the plurality of groups of nozzles being removed by suction through the through-openings.
Still optionally, side surfaces of each of the protrusions may be configured to have water-shedding property.
Further, an upper surface of each of the protrusion may also be configured to have a water-shedding property.
Optionally, an upper surface of each protrusion may be configured to incline upward along a feeding direction of the recording medium.